Method of concentrating fine particle dispersion and method of recovering fine particle

ABSTRACT

A method for concentration of fine particles dispersed in a dispersion into an ionic liquid comprising, adding an ionic liquid, especially an organic ionic liquid at ordinary temperature, e.g., a salt of 1-butyl-3-methylimidazolium with PF 6   −  to a dilute dispersion of fine particles so as to concentrate the fine particles into the ionic liquid.

FIELD OF THE INVENTION

The present invention relates to a method for concentration of fineparticles prepared by adding an ionic liquid, which does not dissolvesubstantially in a dispersing medium, to a dilute dispersion of fineparticles so as said fine particles to transfer to said ionic liquid andto obtain high concentrated dispersion of fine particles and a methodfor recovery of fine particles by filtration of the concentrated fineparticles.

DESCRIPTION OF THE PRIOR ART

As the method for concentration or recovery of fine particles from adispersion characterizing fine particles are dispersed in dilutecondition in dispersing medium, a method to remove basically a liquid,which is a dispersing medium, by evaporation at atmospheric pressure, invacuum, freezing or by adding azeotropic component or a method to removeliquid of dispersing medium by using a membrane filter can be mentioned.A technique that deems to use a membrane filter is announced in internetthat said technique will be reported as “R316; Concentration of fineparticles dispersion using vibrating filtration and size separation”(Shigetoshi Ichimura; Kanagawa Institute of Technique, Shinichi Nakao;Graduated school of Tokyo University, faculty of engineering) at SCEJ68^(th) Annual Meeting.

Problems of environmental contamination are paid attention in variousfields, and accordingly, also in the field of chemistry, establishmentof a method which is gentle to environment is becoming a key point thataffect the existence of a firm.

Regarding said environmental problem, besides a subject not to excludeharmful substances from a chemical reaction system, it becomes necessaryto consider to suppress formation of CO₂ in whole production system,because a regulation to suppress formation of CO₂ becomes more serious.Therefore, regarding a method to remove a dispersing solvent using largequantities of energy, for example, in a case that a dispersing solventis water, since latent heat of evaporation is large, it is necessary todevelop a method to concentrate or separate and recover fine particlesfrom dispersing medium which can be replaced with water.

In above mentioned circumstances, in a chemical reaction, a solvent tobe used has a function not only to control an explosive progress of areaction of reagent, but also has a function to remove heat of reaction,further has a function to accomplish easy handling of the reagent.However, it is necessary to separate and remove said used solvent fromreaction product after chemical reaction. At the separation and removalof said solvent, same problem causes at concentration of said fineparticles dispersion, that is, how to remove and waste large quantity ofsolvent in the condition without a problem of environmentalcontamination.

Thereupon, as a solvent which can dissolve said problem, an ionic liquidis proposed (Thomas Welton, Chem. Rev. 1999, 99, page 2071-2083;Document 1, Hiroaki Sasaki, “Chemical” vol. 55, No. 3, 2000, page 66-67;Document 2). Said ionic liquid is aiming clean chemistry and has widetemperature region for maintaining its liquid state, has smallvolatility, can be a solvent for many reaction reagents and separationand recovery of a reaction product after reaction from it are easy.After said proposal, an ionic solvent composed of combination of anionand cation which can be a solvent usable for a specific reaction hasbeen researched. In particular, a development of organic ionic liquidwhich exaggerates a function as a solvent by improvement of chemicalstructure of cation has been progressed actively (Japan ChemicalSociety, 78^(th) Spring Annual Meeting, Abstract I, lecture 2A1 06“Development of novel ionic liquid and properties thereof”, 2000;Document 3).

As a typical organic ionic solvent, 1-alkylpridinium salt,1-alkyl-3-methylimidazolium salt or ammonium salt represented byfollowing formulae 1a, 1b and 1c can be mentioned as a useful compoundor a compound having useful function.

Wherein, R₃ is an alkyl group, in particular, hexyl group of carbonnumber 1-7, R₁ is an alkyl group, in particular, ethyl group, butylgroup, benzyl group, X⁻ is PF₆ ⁻, BF₄ ⁻, NO₃ ⁻, (CF₃SO₃)₂N⁻, TFSI⁻, orCl⁻.

Cation and anion which form ionic liquid are developed in various ways(Document 1). In above mentioned developments, it is recognized that thecombination with a counter ion is deeply related to properties of ionicliquid, especially to temperature region for maintaining its liquidstate. Ionic liquid, which is also called as an ordinary temperaturefused salt, has an onium salt possessing N, O, P or S as a main elementas an organic cation. Besides said cation, compounds which are convertedto cation by protonation of phosphonium, ammonium salt,2-methyl-1-pyroline, 1-methylpyrazole or 1-ethylcarbazole can bementioned.

However, the ionic liquid has also difficult problem. Vapor pressure ofionic liquid is almost zero, and in a case of reuse of it after used inreaction in the same way to a conventional organic solvent, separationof compound which dissolved in the ionic liquid becomes a problem.Considering said circumstance, a separation method combiningsupercritical CO₂ with ionic liquid is paid attention. Blanchard andBrennecke have reported that imidazolium ionic liquid can dissolvesupercritical CO₂ by 0.6 mole fraction at 8 MPa and when added more themixture separates to two phases. And are further reporting that since inthe separated CO₂ phase the ionic liquid is not detected, the compounddissolved in the ionic liquid is recovered in the CO₂ phase (Blanchard,L. A., Gu, Z., Brennecke, J. F., J. Phhys. Chem. B, 2001, 105,2437-2444: Document 4).

The subject of the present invention is to provide a method forconcentration of dispersion in which fine particles are dispersed indilute condition or recovery of said fine particles, removing abovementioned environmental problem and energy problem at concentration orrecovery of fine particles. In the meanwhile, it is known that fineparticles dispersed in dispersing medium have electric charge indispersing medium.

Said ionic liquid is developed as a substitution of water which isbroadly used as a reaction medium, it can be a solvent of a reactionreagent in reaction system, further, in some cases, is remarkablydistinguished from water at a special feature that reaction material andreaction product can be easily separated and recovered after reaction,because solubility and function to a reaction reagent and a reactionproduct are different by chemical structure of cation and counter anionto be combined with it. Furthermore, it is possible to select asubstance which is insoluble in a dispersing liquid such as water. Stillfurther, it is considered that an ionic liquid has mutual action againstelectric charged component, and when the electric charged component isclosed to the ionic liquid, it causes attracting strength formed bydifference between attractive power against electron charge component oforiginal dispersing medium and attractive power of the ionic liquid.Thereupon, salt of 1-butyl-3-methylimidazolium cation, which is atypical organic ionic liquid, and PF₆ ⁻ is added to dispersion in whichfine particles are dispersed in dilute condition and stirred, and it isfound that the fine particles-are transferred from the dispersing mediumto a liquid phase of organic ionic liquid and concentrated, thus theabove mentioned subject is dissolved.

DISCLOSURE OF THE INVENTION

The present invention is (1) a method for concentration of fineparticles dispersed in a dispersion comprising, adding an ionic liquid,which does not dissolve substantially a dispersing medium of saiddispersion, to said dispersion containing fine particles, transferringsaid fine particles from said dispersion to said ionic liquid andconcentrating said fine particles into said ionic liquid. Desirably, thepresent invention is (2) the method for concentration of fine particlesdispersed in a dispersion of (1), wherein the amount of ionic liquid bmM to be added to 10 mL of the dispersion containing said fine particlesby a mM dispersing concentration is in the range so as the ratio a/b tobe at least 0.05. More desirably, the present invention is (3) themethod for concentration of fine particles dispersed in a dispersion of(1) or (2), wherein the ionic liquid is an ionic liquid which is liquidat ordinary temperature. Further desirably, the present invention is (4)the method for concentration of fine particles dispersed in a dispersionof (3), wherein the ionic liquid is an organic ionic liquid. Furthermoredesirably, the present invention is (5) the method for concentration offine particles dispersed in a dispersion of (4), wherein the organicionic liquid is selected from the group consisting of compoundsrepresented by following formulae 1.

In formulae 1, R₃ and R⁴ are an alkyl group of carbon number 1-7, n isan integer of 1-3, R₁ is an alkyl group which can possess a substitutiongroup of carbon number 1-7, X⁻ is selected from the group consisting ofPF₆ ⁻, BF₄ ⁻, NO₃ ⁻, (CF₃SO₃)₂N⁻, TFSI⁻, Cl⁻ and SO₃H⁻.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention will be explained more in detail.

-   A. In the present invention, as an ionic liquid, public known ionic    liquid can be basically used, however, considering a problem of    energy consumption, an ionic liquid which maintains liquid state at    ordinary condition is preferably used, further considering recovery    process of fine particles after concentration, an ionic liquid of    lower viscosity is preferably used, and when the viscosity is high,    it is possible to add solvent such as ether for the purpose to    reduce the viscosity, then filtrated.

As a desirable ionic liquid, compounds disclosed in above formulae 1 canbe mentioned, and as the most desirable one, imidazolium organic ionicliquid represented by above formula 1 b can be mentioned.

-   B. In a case of aqueous dispersion of fine particles, regarding the    amount of ionic liquid to be added b (mL), which is slightly    affected by temperature of adding liquid and concentration of    dispersion, at the range of dispersion concentration is over than    0.01 mM and at the temperature range of from ordinary temperature to    100° C., when the ratio a/b to fine particles content a (mL) in fine    particles dispersing medium is 0.067 or more, the concentration of    fine particles becomes possible, and smaller than 1 is desirable.    However, in a case of not aqueous dispersion, this definition is not    suited.-   C. For the purpose to concentrate fine particles into ionic liquid,    it is necessary to stir well after the ionic liquid is added.-   D. After fine particles are concentrated in the ionic liquid, the    ionic liquid can be separated by public known filter membrane, for    example, which is disclosed in Japanese Patent Laid Open Publication    10-57784.-   E. As the fine particles, which is subjected by the method for    concentration of the present invention, is the particles whose    particle size is from nano meter to several ten micro meter order,    for example, the particles smaller than 20 micro meter, and not    related to materials composing the particles, for example, can be    applied to pigment, metal, semi-conductor, polymer or composite    materials, or system containing plural components. This fact is    considered to be caused by transferring of fine particles by ionic    liquid, and concentrating action is caused by electric charge    characteristic. However, this method can not be applied to a case    which contains soluble material to an ionic liquid as a material    composing the fine particles.-   F. As a method to recover fine particles from the ionic liquid, a    filtration method which uses above mentioned filtering membrane for    fine particles can be considered. When the viscosity of the ionic    liquid is high, it is possible to add adequate organic solvent so as    to reduce the viscosity, then can be separated by filtration.

EXAMPLE

The present invention will be illustrated more in detail according toReference Examples and Examples, however, not intending to limit thescope of the present invention.

In following Examples 1-6, a salt of 1-butyl-3-methylimidazolium, whichis a typical organic ionic liquid, and PF₆ ⁻ is used as an ionic liquid.

Observation of particles before and after dispersion is carried out byfollowing method.

-   1. Observation of color change by visual inspection.-   2. Observation of shape of particles; observed by an electron    scanning microscope (Hitachi Seisakusho, S-900).

Example 1

Blue coloration aqueous dispersion containing 0.2 mM (conc. a mM) ofvarious size of polydiacetylene fine particles (150 nm, 50 nm, 120 nm,500 nm, fibrous particles of several 10 micrometer) are prepared byreprecipitation method using 1,6-di-(N-carbazoil)-2,4-hexadine(shortened to DCHD). After that, 10 mL of these dispersions are pickedout into sampling bottles at room temperature and every 5-10 drops ofionic liquid (1 drop is approximately 0.01 mL) are added to each bottlesas a coagulation promoter and mixed violently. This process is repeated.When smaller amount of the ionic liquid than 0.1 mL (adding amount ofionic liquid is b mL) is added, phase separation does not occur, on thecontrary, when amount of 0.1 mL to 0.2 mL is added[a(mM)/b(mL)=0.5-1.0], liquid drops of ionic liquid, which coloredslightly blue, appears at the bottom of the bottle. When more than 0.2mL (a/b=1) of ionic liquid is added, color of original dispersionbecomes colorless and transparent and fine particles of polydiacetyleneare almost perfectly recovered in liquid drops of the ionic liquid. Whenthe ionic liquid is further excessively added, size of the liquid dropsbecomes larger. Before and after this process, there are no change inshape of fine particles and photo absorption feature.

Since even if the particle size is changed, adding amount of the ionicliquid necessary for concentration is not changed, dependency of addingamount of ionic liquid to particle size is not recognized.

Example 2

Blue coloration aqueous dispersion containing various concentration(0.01 mM, 0.1 mM, 0.5 mM) of polyacetylene fine particles ofapproximately 100 nm are prepared by reprecipitation method using1,6-di-(N-carbazoil)-2,4-hexadine (shortened to DCHD). After that, 10 mLof these dispersions are picked out into sampling bottles at roomtemperature and every 5-10 drops of ionic liquid (1 drop isapproximately 0.01 mL) are added to each bottles as a coagulationpromoter and mixed violently. This process is repeated. When more than0.1 mL of ionic liquid is added, phase separation occurs and liquiddrops of ionic liquid, which colored slightly blue, appear at the bottomof the bottles. As shown in Table 1, adding amounts necessary forperfect recovery of each concentration are different. Before and afterthe concentration process, there are no change in shape of fineparticles and photo absorption feature. TABLE 1 a; conc. of dispersion/b; necessary adding amount ratio: mM of ionic liquid/mL a mM/b mL 0.010.15 0.067 0.1 0.2 0.5 0.5 0.5 1.0

Example 3

Yellow coloration aqueous dispersion prepared by making perylene nanoparticles (size is approximately 150 nm, fibrous particles of severalmicro meter) contain in 0.1 mM using reprecipitation method is prepared.10 mL of the dispersion is picked out into sampling bottles andmaintained in different temperature conditions (5° C., 18° C., 80° C.),then every 5-10 drops of an ionic liquid (1 drop is approximately 0.01mL) are added to each bottles as a coagulation promoter and mixedviolently. This process is repeated. Yellow colored liquid drops of theionic liquid appear at the bottom of bottles. Necessary amounts of theionic liquid that can confirm the occurrence of phase separation aredifferent by each temperature, and have a tendency that the amountincreases at higher temperature. Necessary adding amounts of ionicliquid for perfect recovery are summarized in Table 2. At 0.1 mMdispersion concentration, temperature: 5° C./necessary adding amount:0.2 ml, temperature: 18° C./necessary adding amount: 0.25 ml,temperature: 80° C./necessary adding amount: 0.3 ml. Before and afterthe operation, there are no change in shape of fine particles and photoabsorption feature. TABLE 2 Conc. of dispersion = 0.1 mM temperature ofnecessary adding amount of ratio: dispersion/° C. ionic liquid b (mL) amM/b mL  5° C. 0.2 0.5 18° C. 0.25 0.4 80° C. 0.3 0.33

Example 4

Colored aqueous dispersion prepared by making particles of cupperphthalocyanine (size: approximately 100 nm), quinacridone (size:approximately 100 nm), C60 (size: approximately 270 nm) or polystyrene(size: approximately 200 nm) contain in 0.1 mM using reprecipitationmethod is prepared. 10 mL of these dispersions are picked out intosampling bottles at room temperature and every 5-10 drops of an ionicliquid (1 drop is approximately 0.01 mL) are added to each bottles as acoagulation promoter and mixed violently. This process is repeated. In acase when more than 0.15 ml of ionic liquid is added, phase separationis caused and liquid drops of colored ionic liquid appear at the bottomof bottle. Necessary adding amount for perfect recovery to eachdispersions are equally 0.2 ml as shown in Table 3. Before and after theoperation, there are no change in shape of fine particles and photoabsorption feature. TABLE 3 Conc. of dispersion = 0.1 mM necessaryadding amount of ionic ratio: dispersed material size/nm liquid b (mL) amM/b mL cupper 100 0.15-0.2 0.67-0.5 phthalocyanine quinacridone 1000.15-0.2 0.67-0.5 fullerene C₆₀ 270 0.15-0.2 0.67-0.5 polystyrene 2000.15-0.2 0.67-0.5

Example 5

To 10 ml of colored aqueous dispersion prepared by making particles ofsilver (size: approximately 30 nm), gold (size: approximately 20 nm),cadmium sulfide (size: approximately 300 nm) or titanium dioxide (size:approximately 20 nm) contain in 2 mM at room temperature, every 5-10drops of an ionic liquid (1 drop is approximately 0.01 ml) are added toeach bottles as a coagulation promoter and mixed violently. This processis repeated. When more than 0.15 ml of the ionic liquid is added, phaseseparation is caused and liquid drops of colored ionic liquid appear atthe bottom of bottle. Especially, in cases of fine particles of gold andsilver, metallic luster is recognized. Necessary adding amount forperfect recovery to each dispersions are equally 0.2 ml as shown inTable 4. Before and after the operation, there are no change in shape offine particles and photo absorption feature. TABLE 4 Conc. of dispersion= 0.1 mM necessary adding amount of ionic ratio: dispersed materialsize/nm liquid b (mL) a mM/b mL silver 30 0.15-0.2 0.67-0.5 gold 200.15-0.2 0.67-0.5 CdS 300 0.15-0.2 0.67-0.5 TiO₂ 20 0.15-0.2 0.67-0.5

Example 6

To 10 mL of cyclohexane dispersion in which 2.0 wt % of particles ofpolyimide (size: approximately 250 nm) is contained, every 5-10 drops ofan ionic liquid (1 drop is approximately 0.01 ml) are added as acoagulation promoter and mixed violently at room temperature. When morethan 0.15 ml of the ionic liquid is added, phase separation is causedand liquid drops of colored ionic liquid appear at the bottom ofbottles. However, necessary adding amount for perfect recovery isapproximately 1.5 mL and is larger when compared with an aqueousdispersion. Before and after the operation, there are no change in shapeof fine particles and photo absorption feature.

INDUSTRIAL APPRICABILITY

As mentioned above, by use of ionic liquid, an excellent effect thatfine particles contained in diluted dispersion can be effectivelyconcentrated in the ionic liquid is provided, and has a bright featureas a concentration technique of industrial scale.

1. A method for concentration of fine particles dispersed in adispersion comprising, adding an ionic liquid, which does not dissolvesubstantially a dispersing medium of said dispersion, to said dispersioncontaining fine particles, transferring said fine particles from saiddispersion to said ionic liquid and concentrating said fine particlesinto said ionic liquid.
 2. The method for concentration of fineparticles dispersed in a dispersion of claim 1, wherein the amount ofthe ionic liquid b mM to be added to 10 mL of the dispersion containingsaid fine particles by a mM dispersing concentration is in the range soas the ratio a/b to be at least 0.05.
 3. The method for concentration offine particles dispersed in a dispersion of claim 1, wherein the ionicliquid is an ionic liquid which is liquid at ordinary temperature. 4.The method for concentration of fine particles dispersed in a dispersionof claim 3, wherein the ionic liquid is an organic ionic liquid.
 5. Themethod for concentration of fine particles dispersed in a dispersion ofclaim 4, wherein the organic ionic liquid is selected from the groupconsisting of compounds represented by following formulae 1,

wherein, R₃ and R⁴ are an alkyl group of carbon number 1-7, n is aninteger of 1-3, R₁ is an alkyl group which can possess a substitutiongroup of carbon number 1-7, X⁻ is selected from the group consisting ofPF₆ ⁻, BF₄ ⁻, NO₃ ⁻, (CF₃SO₃)₂N⁻, TFSI⁻, Cl⁻ and SO₃H⁻.
 6. The methodfor concentration of fine particles dispersed in a dispersion of claim1, wherein the ionic liquid to be added to the dispersion containingfine particles is an ionic liquid which is liquid at ordinarytemperature and the amount of the ionic liquid b mM to be added to 10 mLof the dispersion containing said fine particles by a mM dispersingconcentration is in the range so as the ratio a/b to be at least 0.05.7. The method for concentration of fine particles dispersed in adispersion of claim 6, wherein the ionic liquid is an organic ionicliquid.
 8. The method for concentration of fine particles dispersed in adispersion of claim 7, wherein the organic ionic liquid is selected fromthe group consisting of compounds represented by above mentionedformulae
 1. 9. The method for concentration of fine particles dispersedin a dispersion of claim 2, wherein the ionic liquid is an ionic liquidwhich is liquid at ordinary temperature.
 10. The method forconcentration of fine particles dispersed in a dispersion of claim 9,wherein the ionic liquid is an organic ionic liquid.
 11. The method forconcentration of fine particles dispersed in a dispersion of claim 10,wherein the organic ionic liquid is selected from the group consistingof compounds represented by following formulae 1,

wherein, R₃ and R⁴ are an alkyl group of carbon number 1-7, n is aninteger of 1-3, R₁ is an alkyl group which can possess a substitutiongroup of carbon number 1-7, X⁻ is selected from the group consisting ofPF₆ ⁻, BF₄ ⁻, NO₃ ⁻, (CF₃SO₃)₂N⁻, TFSI⁻, Cl⁻ and SO₃H⁻.